21573815807 has 4 divisors (see below), whose sum is σ = 22317740520. Its totient is φ = 20829891096.

The previous prime is 21573815719. The next prime is 21573815843. The reversal of 21573815807 is 70851837512.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21573815807 - 2⁸ = 21573815551 is a prime.

It is a super-2 number, since 2×21573815807² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21573817807) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 371962313 + ... + 371962370.

It is an arithmetic number, because the mean of its divisors is an integer number (5579435130).

Almost surely, 2^21573815807 is an apocalyptic number.

21573815807 is a deficient number, since it is larger than the sum of its proper divisors (743924713).

21573815807 is an equidigital number, since it uses as much as digits as its factorization.

21573815807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 743924712.

The product of its (nonzero) digits is 470400, while the sum is 47.

The spelling of 21573815807 in words is "twenty-one billion, five hundred seventy-three million, eight hundred fifteen thousand, eight hundred seven".